Detection and Localization of Terrestrial L-Band RFI with GNSS Receivers

GNSS signals are critically important for a widerange of commercial, military, and science applications. Recentstudies have identified threats to the performance of GNSSfrom both intended and unintended sources of radio frequencyinterference (RFI). Understanding the distribution of the sourcesof RFI and the nature of the signals they are emitting is critical todetermine and mitigate their effects on the measurements madeby GNSS receivers. Terrestrial RFI can be substantially detrimental to the received GNSS signals, affecting the interpretationof related science measurements. NASA’s Blackjack/TriG GNSSreceivers are used for precise-orbit determination and radiooccultation measurements, providing a data record spanningmost of the Earth’s surface for nearly 20 years. We havedeveloped a highly sensitive detection algorithm which usesvariations in the measured signal to noise ratio (SNR), on theorder of 10-50 seconds, common to all satellites to identify timesand locations subject to RFI. Initial work has focused primarilyon detection of the presence of RFI and using the receiver’sorbital solution to record the location of detection events. Ourinter-mission analysis creates a unique record of global RFIwith the potential for a) rigorous detection of the presence ofinterfering signals during science measurements, b) geolocationof RFI sources, and c) characterization of the nature of thetransmitted signal to better identify intent. Preliminary analysishas shown the presence of RFI is well correlated with regionalconflicts and other geopolitical activity.